Here are two articles pointing out weaknesses in Bitwarden's architecture that are very similar to those discovered with LastPass. They describe apparent weaknesses in the vault encryption architecture and the use of PBKDF2 with a relatively low iteration count for master passwords.
palant.info
There is also a reddit thread discussing these, in which one developer states that Bitwarden is working to address these issues. But others are saying the issues have been known for a while with no action from Bitwarden.
This seems significant given that many left LastPass for Bitwarden due to LastPass's similar issues. I'd be interested to hear people's thoughts.

Bitwarden design flaw: Server side iterations
Bitwarden is a hot candidate for a LastPass replacement. Looking into how they encrypt data, it doesn’t do things that much better however.
There is also a reddit thread discussing these, in which one developer states that Bitwarden is working to address these issues. But others are saying the issues have been known for a while with no action from Bitwarden.
This seems significant given that many left LastPass for Bitwarden due to LastPass's similar issues. I'd be interested to hear people's thoughts.